I know my bumper may very well have been replaced before I got the car in 1975, but my car was a '350' car and it has the arrowhead in the bumper. Just to throw that out there.
I think that the tri-power cars had the bumper emblem too. Gotta tell this story one more time; Back in 1986 I bought a 69 350 car. Cloned it all out to a 400. Changed the hood, added every detail to make it a 400 car. Finally, it was all done in '88. I decided to get the PHS paperwork just for grins. The PHS build sheet said it was originally a 400 car! Goes to show that these cars go through a lot of 'changes' over the years. Some owners are very ambitious and can do just about anything to their car and sometimes the changes can be many.